I noticed the new iMac has an x after the video card versus the 2017 model. So is the 570X in the 2019 iMac the same as the 570 in the 2017 iMac and is the X just there to confuse me or is there a performance boost if so how much? Otherwise I might just pick up a refurbished model from 2017 if there is no difference in the video.